1. Field of the Invention
The present invention relates to an image sensing apparatus having a camera shake detection function and a camera shake correction function, and a control method, a program, and a storage medium of the image sensing apparatus.
2. Description of the Related Art
It is conventionally known that in an image sensing apparatus such as a digital camera, the shift amount due to camera shake is detected by photographing a plurality of frame images, and correlating data of the obtained frame images. In this case, it has been also proposed that the data of the plurality of frame images be synthesized while being shifted based on the detection results, thereby performing electronic camera shake correction for correcting blurring of an image caused by camera shake. In contrast to an optical camera shake correction system, in this type of electronic camera shake correction, an optical system drive section for driving an optical system is not necessary, and thus the image sensing apparatus can be made smaller.
For example, as shown in FIG. 11, in a proposed electronic camera shake correction system, the image sensing apparatus is provided with a first memory 200 and a second memory 202. A calculating section 201 detects a motion vector of an object image in a characteristic area between frame image data 203 successively photographed and respectively accumulated in the first memory 200 and the second memory 202. The thus detected motion vector is output from a motion vector output section 204. Then, as shown in FIG. 12, sequentially captured frame image data is subjected to an adding process while being shifted in the direction opposite to the camera shake direction based on the detected motion vector. Japanese Patent Laid-Open No. 2005-328326 has disclosed a technique for obtaining, in a synthesizing memory 205, image data for one frame on which the camera shake correction has been performed.
A plurality of frame memories is necessary in the electronic camera shake correction illustrated in FIG. 11. However, it is also possible that as shown in FIG. 13, in a memory 300 having a frame memory area larger than one frame, a plurality of frame image data that have been sequentially captured are superimposed one on another while being shifted based on camera shake shift information obtained by a shift amount detecting device. Japanese Patent Laid-Open No. 2005-328326 has disclosed a technique for performing camera shake correction with one image synthesizing memory.
In the electronic camera shake correction, one frame image data is obtained from a plurality of frame image data that have been obtained by photographing an image by performing a plurality of exposures. Thus, it is necessary to adjust the signal level when synthesizing the plurality of frame image data. For example, Japanese Patent Laid-Open No. 2003-259208 has disclosed a technique for performing camera shake correction by synthesizing a plurality of sequentially shot frame image data whose signal level has been adjusted.
In Japanese Patent Laid-Open No. 2005-328326, a plurality of frame image data are superimposed one on another while being shifted based on the results of camera shake detection. Thus, in a case where images are shot at underexposure, the signal level varies depending on how the frame image data are superimposed. Accordingly, when extracting image data whose signal level has been corrected, the area from which images can be extracted is limited. Furthermore, even in a case where images are captured while exposure is made appropriate for each frame image, the signal level for each frame image data is low, because the images are photographed by performing a plurality of exposures in a short time. Thus, even if the signal level is increased in order to make the signal level of the image data appropriate, the S/N of each image data is low, and noise components are amplified in the corrected image data that is to be extracted.
In Japanese Patent Laid-Open No. 2003-259208, in image synthesis, image data are synthesized while the signal level is adjusted. At that time, the plurality of frame image data that have been sequentially captured are added while being shifted for camera shake correction. Thus, as in Japanese Patent Laid-Open No. 2005-328326, the number of image data superimposed varies from image area to image area, and the signal level is not uniform throughout the entire area of the synthesized image. Thus, image data that can be extracted at the same signal level has a size smaller than the effective pixel area.